Since the 1930s it has been known that injury or ablation of the sympathetic nerves in or near the outer layers of the renal arteries can dramatically reduce high blood pressure. At the present time, physicians often treat patients with atrial fibrillation (AF) using radiofrequency (RF) catheter systems to ablate conducting tissue in the wall of the left atrium of the heart around the ostium of the pulmonary veins. Similar technology, using radiofrequency energy, has been successfully used inside the renal arteries to ablate sympathetic and other nerve fibers that run in the outer wall of the renal arteries, in order to treat high blood pressure. In both cases these are elaborate and expensive catheter systems that can cause thermal, cryoablative, or other methods to injure surrounding tissue. Many of these systems also require significant capital outlays for the reusable equipment that lies outside of the body, including RF generation systems and the fluid handling systems for cryoablative catheters.
Because of the similarities of anatomy, for the purposes of this disclosure, the term target wall will refer here to either the wall of the left atrium surrounding a pulmonary vein or the wall of a pulmonary vein near its ostium for AF ablation applications or the wall of the aorta around the ostium of the renal artery, or within the renal artery itself, for hypertension or congestive heart failure (CHF) applications.
In the case of atrial fibrillation ablation, the ablation of tissue surrounding multiple pulmonary veins can be technically challenging and very time consuming. This is particularly so if one uses RF catheters that can only ablate one focus at a time. There is also a failure rate using these types of catheters for atrial fibrillation ablation. The failures of the current approaches are related to the challenges in creating reproducible circumferential ablation of tissue around the ostium (peri-ostial) of a pulmonary vein. There are also significant safety issues with current technologies related to very long fluoroscopy and procedure times that lead to high levels of radiation exposure to both the patient and the operator, and may increase stroke risk in atrial fibrillation ablation.
There are also potential risks using the current technologies for RF ablation to create sympathetic nerve denervation from inside the renal artery for the treatment of hypertension or congestive heart failure. The short-term complications and the long-term sequelae of applying RF energy from inside the renal artery to the wall of the artery are not well defined. This type of energy applied within the renal artery, and with transmural renal artery injury, may lead to late restenosis, thrombosis, renal artery spasm, embolization of debris into the renal parenchyma, or other problems inside the renal artery. There may also be uneven or incomplete sympathetic nerve ablation, particularly if there are anatomic anomalies, or atherosclerotic or fibrotic disease inside the renal artery, such that there is non-homogeneous delivery of RF energy This could lead to treatment failures, or the need for additional and dangerous levels of RF energy to ablate the nerves that run along the adventitial plane of the renal artery.
The currently used system for RF energy delivery also does not allow for efficient circumferential ablation of the renal sympathetic nerve fibers. If circumferential RF energy were applied in a ring segment from within the renal artery (energy applied at intimal surface to kill nerves in the outer adventitial layer) this could lead to even higher risks of renal artery stenosis from the circumferential and transmural thermal injury to the intima, media and adventitia. Finally, the “burning” or the inside of the renal artery using RF ablation can be extremely painful. Thus, there are numerous and substantial limitations of the current approach using RF-based renal sympathetic denervation.
The Bullfrog® micro infusion catheter described by Seward et al in U.S. Pat. Nos. 6,547,803 and 7,666,163 which uses an inflatable elastic balloon to expand a single needle against the wall of a blood vessel could be used for the injection of an chemical ablative solution such as alcohol but it would require multiple applications as it does not describe or anticipate the circumferential delivery of an ablative substance around the entire circumference of the vessel. The most number of needles shown by Seward is two and the two needle version of the Bullfrog® would be hard to miniaturize to fit through a small guiding catheter to be used in a renal artery. If only one needle is used, controlled and accurate rotation of any device at the end of a catheter is difficult at best and could be risky if the subsequent injections are not evenly spaced. This device also does not allow for a precise, controlled, and adjustable depth of delivery of a neuroablative agent. Another limitation of the Bullfrog® is that inflation of a balloon within the renal artery can induce stenosis due to balloon injury of the intima and media of the artery, as well as causing endothelial cell denudation.
Jacobson and Davis in U.S. Pat. No. 6,302,870 describe a catheter for medication injection into the inside wall of a blood vessel. While Jacobson includes the concept of multiple needles expanding outward, each with a hilt to limit penetration of the needle into the wall of the vessel, his design depends on rotation of the tube having the needle at its distal end to allow it to get into an outward curving shape. The hilt design shown of a small disk attached a short distance proximal to the needle distal end has a fixed diameter which will increase the total diameter of the device by at least twice the diameter of the hilt so that if the hilt is large enough in diameter to stop penetration of the needle, it will significantly add to the diameter of the device. For either the renal denervation or atrial fibrillation application, the length of the needed catheter would make control of such rotation difficult. In addition, the hilts which limit penetration are a fixed distance from the distal end of the needles. There is no built in adjustment on penetration depth which may be important if one wishes to selectively target a specific layer in the blood vessel or if one needs to penetrate all the way through to the volume past the adventitia in vessels with different wall thicknesses. Jacobson also does not envision use of the injection catheter for denervation. Finally, Jacobson in FIG. 3 when he shows a sheath over expandable needles, there is no guide wire and the sheath has an open distal end which makes advancement through the vascular system more difficult. Also the needles if they were withdrawn completely inside of the sheath they could because of the hilts, get stuck inside the sheath and be difficult to push out.
The prior art also does not envision use of anesthetic agents such as lydocaine which if injected first or in or together with an ablative solution can reduce or eliminate any pain associated with the denervation procedure.
Finally, while injection of ethanol as an ablative substance is well known and used within the heart and other parts of the body, there has been no development of an ethanol (or other liquid nerve ablation substances) injection system specifically designed for the circumferential ablation of sympathetic nerve fibers around the renal arteries.